A. Field of the Invention
This invention relates to the art of constructing buildings, especially relatively small and low cost residential, institutional and commercial buildings, utilizing modular prefabricated structural members therefor. More specifically, this application pertains to a novel apparatus and method for prefabricating the structural members.
B. Background of the Invention
Small buildings today are constructed using methods developed before the Industrial Revolution. These types of buildings, as opposed to steel frame building types, are constructed either by cutting up trees into boards of different sizes and nailing the boards together or by erecting stacks of stone or masonry held together with mortar. Historically, such raw materials have been delivered to the construction sites where they are then made into buildings by the process of assembling the cut-up parts of the trees and/or the blocks of stone or masonry into simple xe2x80x9cpost and beamxe2x80x9d type structures the parts of which work independently of one another.
Heretofore, it has been attempted, with a good deal of progress having been made in the more recent past, to achieve factory production of buildings in various forms of modular, panelized and mobile home unit construction, but these never were and still do not represent and embody new technologies; they are simply examples of the same historical xe2x80x9cpost and beamxe2x80x9d technology executed indoors-off-site instead of outdoors-on-site. However, although some cost savings may have been achieved through the use of modern techniques such as bulk raw material purchasing and through the utilization of newer and faster tools, the final products have not only remained basically the same but, because labor and materials are still being used inefficiently, are vulnerable to damage and destruction by fire, hurricanes, earthquakes, moisture and insects.
Building codes, which in the United States serve as minimum standards of construction quality, actually tend to exacerbate these inefficiencies by trying to mandate better quality and greater safety of buildings while anticipating the mediocre labor skills currently found on construction sites. Architects and engineers tend to design buildings in light of the government-specified parameters and then follow up by specifying the use of the already available construction materials and methods. This not only reinforces the use of existing methods but also inhibits innovation in building construction. The construction industry tolerates these disadvantages because a better way has not yet been found and perfected.
The availability and price of lumber have changed drastically over the past decade or so, with availability decreasing and price increasing. The deleterious results of indiscriminate tree cutting are giving rise to alarm over the ecological consequences of global deforestation and have led to great pressure, primarily from environmental groups around the world, on forest products companies and governments to control and slow down such activity. As a consequence, lumber has become increasingly more expensive as distances from source to destination increase transportation costs. Furthermore, skilled craftsmen such as carpenters and masons currently command very high salaries and, even worse, are neither as abundant nor as skilled as they once were. In sum, therefore, small buildings being currently constructed make inefficient use of raw materials, cost more to build, operate and maintain than is necessary, are highly combustible, and are expensive to reinforce to mitigate the threats of fire, earthquakes, hurricanes and floods.
An objective of the present invention is to provide a fixture that can be used to assemble a modular type structural member quickly and effectively.
A further objective is to provide a fixture which may be easily adapted to assemble or prefabricate modular structural members of various sizes and shades.
A further objectives and advantages is to provide a fixture which can assemble a structural member automatically.
In the above-mentioned co-pending application Ser. No. 09/223,666 a class of novel prefabricated hollow shell-type modular structural members is described, each of which members includes a triangulated wire core disposed between and secured to a pair of spaced shell panels defining the faces of the structural member, and which members are adapted, in appropriate forms and strengths, for serving as foundations, walls, floors, roofs and partitions of low cost, relatively small buildings. The modular structural members which, in their manufactured form, are adapted to be easily assembled and interconnected at the construction site so as to define both the structural configuration of the building (including its doors, windows and surface finishes) as well as the infrastructure for its life support systems (including its plumbing systems, electrical systems, heating, ventilation and air conditioning systems, fire protection systems, etc.) as the building is being erected.
A plurality of such modular structural members can be used per se either to form a complete self-contained building or to form a part of or an adjunct to an existing building for purposes of renovation and/or expansion, and which can also be used in conjunction with conventional building materials (steel, concrete and wood) to form composite building structures.
Generally speaking, the fundamental concept of the modular structure which is incorporated in the modular structural members disclosed herein and which may be briefly described as follows.
The strength of any structure results from a combination of the materials of which it is made and the shape or geometry of those materials. Stated in other words, strength is a function not only of the physical properties of the materials which are used but also of the manner in which they are used, i.e., of their geometric configurations.
A force applied to the top apex of a triangular structure will channel down the two sides of the triangle to the two points or apexes at the bottom. The two points at the bottom of the triangular structure will tend to be pushed outward by that force, i.e., away from each other, unless they are restrained and held in place. It is the bottom member of the triangular structure, of course, which holds those two points in place. This is an efficient system because (1) each member is in either simple tension or simple compression as the force imposed at the top of the triangular structure is resisted by the three members and as the load is transferred to the associated supports, and (2) the connections of the three members can be simple because they do not have to be strong enough to resist turning or bending.
It will also be understood that if several triangular structures are grouped together, the force applied thereto will be distributed throughout an appropriately larger number of members. For example, if a four-sided pyramidal arrangement of triangular structures is used instead of a single triangular structure, the applied force is distributed between eight members instead of three. Such an arrangement obviously increases the efficiency of the system.
It will further be understood that multiple pyramidal arrangements of triangular structures can be interconnected with each other horizontally and vertically as well. In such a system, as the number of connected pyramidal arrangements of triangular structures increases, the forces applied thereto in one area are distributed over a large network of members. Moreover, the individual members need not be very strong, since they work together. Thus, a large number of small members can coact to carry large loads, and by using the same size member repeatedly, a very large structure can be constructed.
In practical applications, the tops and bottoms of such triangular structures either per se or in pyramidal arrangements thereof can be individual members or they can be extensive flat plates. If they are plates, then they can form the solid faces of walls, floors, ceilings and roofs required to enclose building structures and their interior spaces. The plates transmit pressure loads applied to the surfaces of these plates to the network of frame members, in addition to resisting the forces in the top and bottom chords of the pyramids.
By applying the efficiencies of these principles to an entire structure, a building constituted by modular structural members according to the present invention can be made to be much stronger than one constructed by conventional methods. For small to medium-size buildings, the forces at the connections between the modular structural members will be small, which will permit simple connections. Using concrete as a covering for the shell panels of the structural members will result in buildings which will not burn.
For the purposes of clarity, by way of definition a building constructed of modular structural members according to the present invention may be considered as consisting of xe2x80x9ccomponentsxe2x80x9d, xe2x80x9celementsxe2x80x9d and xe2x80x9ccellsxe2x80x9d. The components are the general working units or building blocks of the desired end product and are used for forming the foundation of the building structure as well as the walls, the floors, the roof and the interior partitions thereof. They are made in large sizes of up to 40 feet by 12.5 feet (12.2 m by 3.8 m) and in thicknesses from 4.5 inches to 1.5 feet (11.4 cm to 45.7 cm). The xe2x80x9celementsxe2x80x9d are smaller parts of a building including items such as windows, doors, cabinets, closets, and stairs. The xe2x80x9ccellsxe2x80x9d are full building volumes which are prefabricated assemblies of components and elements such as entry foyers, bathrooms, and kitchens. In a building structure of the present invention, the components and cells are uniquely interconnected.
The components, elements and cells are designed to enable various materials to work together synergetically to perform the various functions required of the building. The technology underlying and incorporated in the system of the present invention facilitates both low volume manual and high volume automated manufacturing applications.
The components, i.e., the various modular structural members, are preferably fabricated from the same basic materials and by the same techniques. Each component has a block-like form which consists of two spaced parallel shell panels defining the sides and faces of the block and of an inner portion or core between the shell panels. In all components, the core between the associated two shell panels basically consists of a triangulated wire frame to which the shell panels are secured. To the extent there are any differences between some of the components, these differences are in the structural strengths, the architectural design details, and the thermal performance properties of the components.
The structural strength of each component varies by virtue of differences in the triangulation, the thickness, and the nature and strength of the material of which the xe2x80x9cwirexe2x80x9d of the wire frame is made (the material used for the xe2x80x9cwirexe2x80x9d may be steel, structural plastic, or any other comparable linear material); the material strength of the shell panels; and the depth or thickness of the component. The wire frame consists of zig-zag shaped wire xe2x80x9ctrussesxe2x80x9d placed next to each other in the space between the shell panels and having their tips or apexes connected. The arrangement in particular is such that in each group of three adjacent wire trusses, the middle one thereof has its bottom apexes connected to the bottom apexes of the wire truss located on one side of the middle wire truss and has its top apexes connected to the top apexes of the wire truss located on the other side of the middle wire truss.
In addition, at each of the inside faces of the shell panels bounding the core-accommodating space therebetween, there are provided a set of mutually parallel first wire cables or chord members each of which extends along and is connected to the apexes of a respective one of the wire trusses in a direction parallel to the longitudinal axis of the wire core, and a set of likewise mutually parallel second wire cables or chord members each of which extends perpendicular to the first chord members and is connected thereto at irs intersections with the first chord members and the respective apexes of the various wire trusses. A plurality of anchors located at those intersections connect the chord members and the apexes of the wire trusses to the shell panels.
The shell panels can be made from a variety of materials including concrete, metal, combinations thereof, or other rigid panel material. The most typical is a layer of concrete into which the anchors are embedded. The concrete layer, which is about 2 inches (5.1 cm) thick, may be reinforced with plastic fibers and may additionally be reduced in weight by being transformed into cellular concrete through the incorporation therein of many small air bubbles or a cellular plastic foam. The shell casting material may vary in strength from 150 to 4,000 pounds per square inch (psi) in density from 30 to 120 pounds per cubic foot, as well as in insulating properties. These different shell panel characteristics result from variations in the proportions of the ingredients of the shell mixture that includes cement, sand, reinforcing fibers, and cellular foam. The shell panels are formed to provide the final exposed finish and texture thereof and, in conjunction with the wire frame core, to impart to the modular structural members the required structural load-bearing capacity.
For certain conditions, a metal shellpan may be embedded in the concrete shell panel. The shellpan is designed to provide additional strength, so as to enable the component to accommodate ducts or conduit for electrical wiring or to accommodate reinforcements for openings, holes to receive fasteners at the positions of various life support system parts, etc.
The thickness or diameter of the wire used to form the wire trusses varies from xe2x85x9 inch (0.32 cm) to xc2xd inch (1.3 cm), and its strength varies further according to the strength of the material from which the wire is made. Moreover, as already pointed out, the apexes of the wire truss triangles are fastened to the perpendicularly intersecting first and second chord members and jointly therewith to the shell panels (and, where applicable, to the shellpans as well). The completed wire frame thus is a deep, three dimensional, open xe2x80x9cmeshxe2x80x9d consisting of interconnected triangulated shapes formed by small diameter lightweight wire. As a result, the shell panels and the wire frame members all work together to transfer and resist the forces acting on the various components.
The overall depth or thickness of the structural members will vary from 4xc2xd inches (11.4 cm) in the case of a partition-forming component to 16 inches (40.6 cm) in the case of a large floor-forming component. Typically, as the depth increases, the wire size or thickness of the wire trusses will also increase. The greater depth, of course, increases the capacity of the structural member to resist loads perpendicular to its face (e.g., wind load for walls, floor load for floors, snow load for roofs).
Each modular structural member according to the present invention, therefore, becomes a complete, structurally integral unit. A wall-forming structural member or component actually performs structurally as a large beam (the height of a wall). Tension loads (pulling up on walls) thus are resisted by the entire length of the wall since, the stress from any one point is to be distributed throughout the entire wall-forming component by the interior wire frame. Correspondingly, a floor-forming component acts as a two way-slab spanning up to approximately 24 feet (7.3 m). As such, they are less vulnerable than conventional structures to failure when a section of continuous support is lost, such as due to foundation failure. The substantial portion of structural material is positioned on the outer faces of the component where the greatest efficiency can be attained in all conditions, including the most demanding ones.
In a finished building, furthermore, where the components are connected, the floor-forming components are connected to and supported by the wall-forming components in a way that is different from typical comparable structures. Floors of most conventional structures are supported on beams or joists which themselves are simply supported at their ends by the walls. While the walls do their job supporting the floor load which is brought to them by the floor, they do not help the floor in its job of supporting the weight of the floor load. The floor-forming components in a building according to the present invention are connected to the wall-forming components in a way that enables the walls to help the floor carry its load. The top and bottom shell panels of the floor-forming components are connected to the wall-forming components in a fashion establishing a moment connection between them.
More particularly, in the system of the present invention, at the regions of the floor-to-wall connections the triangulation of the wire trusses, i.e., the spacing of adjacent wire trusses from each other as well as the spacing of adjacent apexes thereof from each other, in the wall-forming components is more compact, which makes the connections stronger and helps the floor-forming component resist its tendency to bend under the load. Each such floor-to-wall connection is continuous along the entire perimeter of the floor-forming component. This substantially increases the load-bearing capacity of the floor-forming components as well as the wind load-bearing capacity of the wall-forming components. For example, engineering calculations indicate that the load-bearing capacity of an 18.8 square foot floor-forming component increases from 60 to 90 pounds per square foot by this connection method.
Furthermore, this changes the nature of the entire assembled structure. Instead of the building being an assembly of independent pieces (studs, joists, or blocks), it becomes a complete whole structural element. This provides excellent resistance to earthquakes, hurricanes and floods.
Advantageously, the structural member is assembled or prefabricated on a fixture formed of a plurality of posts. The posts have a holder at one end adapted to hold the several chords and other members defining a joint. At the opposite end, the posts are mounted on a structure including post rails which may be movable on rail guides. The post rails are used to move the posts and the chords attached thereto to a coupling member such as a welding gun. The coupling member permanently couples or secures the chords together to form the respective joints.
The posts can be formed into a three dimensional lattice defining the dimensions of the structural member. A plurality of guns may be provided to weld several joints simultaneously. In an advantageous arrangement the rail posts move toward the guns and the guns are activated when respective sensors detect the holders with the chords. In this manner the process, or at least the welding of the chords together is easily automated.